Normally all parts of a bicycle frame are firmly interconnected as by welding or soldering, except the steering handle together with the front wheel fork which are pivotable about an almost vertical axis. The pedals are rotatably mounted on crank arms fixed to the shaft of the driving sprocket wheel of the chain drive.
There are further known many complicated two-wheeled vehicles which are intended to make better use of the forces exerted by the driver's arms and legs when they are moved, e.g. in the form of movements similar to those of a rower. Normally, in these cases there is still a rigid frame with additional levers, racks and gears for transmitting torque to one of the wheels.
It is the purpose of this invention to provide a two-wheeled vehicle which is essentially as simple as a bicycle, imitates the movement of riding on horseback or rocking in a harmonic swing and consequently creates the illusion that riding at a certain speed is easier than with a normal bicycle.
It is another purpose of this invention to provide a two-wheeled vehicle with an articulated frame in which all frame members are used as cooperating levers for transmitting the forces from the driver's legs and arms and mainly from his weight to the driven wheel.
A main feature of the present invention includes a frame comprising four pivotably interconnected main frame members of which the upper frame member carries a saddle, the front frame member is provided with a bearing for a steering handle and a front wheel fork, the lower frame member is supported as a rocker on the axle of a rear wheel and is provided with a bearing for a driving sprocket wheel of a chain drive transmitting torque to the rear wheel, and the rear frame member is a link between the upper and lower frame members. It further includes pedals connected to the front or lower frame member, a crank arm fixed to the driving sprocket wheel and a connecting rod between the crank arm and the upper frame member.
The operation of a vehicle constructed in accordance with the present invention can best be understood if it is recognized that the axis of the driving sprocket wheel rotates about the joint between the crank arm and the connecting rod. In a first phase of two cyclically alternating phases of movement the driver, by shifting his weight unto the pedals and unburdening the saddle, presses the axis of the sprocket wheel downwards in relation to the joint between the crank arm and the connecting rod. In the second phase the driver, by shifting his weight onto the saddle and unburdening the pedals, cause the rear frame member to pivot the lower frame member counterclockwise thereby lifting the axis of the driving sprocket wheel in relation to the joint between the crank arm and the connecting rod. The aforementioned forces exerted by weight of the driver are augmented by the driver pulling at the steering handle during the first phase and pushing the steering handle forward during the second phase.
The rotation of the axis of the driving sprocket wheel about the joint between the connecting rod and the crank arm is accompanied by a rotation of the sprocket wheel about its own axis which is transmitted via the chain to the hub of the rear wheel as is conventional. At the same time the crank arm and the connecting rod produce a toggle motion which causes the principally quadrangular articulated frame alternatively to stretch and to contract in diagonal directions that lift and lower the saddle and the pedals reciprocally and move the steering handle forth and back in the driving direction. These movements give a cyclist the impression of riding on horseback.